WO2021075648A1

WO2021075648A1 - Fiber-type strain sensor having core-shell structure, and manufacturing method therefor

Info

Publication number: WO2021075648A1
Application number: PCT/KR2020/003915
Authority: WO
Inventors: 김성수; 온승윤
Original assignee: 한국과학기술원
Priority date: 2019-10-18
Filing date: 2020-03-23
Publication date: 2021-04-22
Also published as: CN113015883B; CN113015883A; KR102297044B1; US11280688B2; US20210404892A1; KR20210046522A

Abstract

The present invention relates to a fiber-type strain sensor having a core-shell structure, and a manufacturing method therefor, and the fiber-type strain sensor having a core-shell structure, of the present invention, comprises: a fiber support constituting a core; and a multi-layer structured shell layer formed on the fiber support, and thus the present invention can manufacture a fiber-type sensor having improved strength and stiffness due to a core fiber, having a reduced noise level due to an elastomer layer, and having improved linearity of a measured signal due to a sandwiched-structured conductive layer, thereby enabling stable measurement of strain while not operating defectively in a composite structure.

Description

Core-shell structure fibrous strain sensor and manufacturing method thereof

The present invention relates to a fibrous strain sensor having a core-shell structure and a method for manufacturing the same, and more particularly, strength and rigidity are improved by a core fiber, a noise level is improved by an elastomer layer, and a conductive layer of a sandwich structure It relates to a fiber-type strain sensor having a core-shell structure having an effect of improving the linearity of a measurement signal and a method of manufacturing the same.

Due to various properties such as excellent specific strength, specific rigidity, and attenuation of fiber-reinforced composite materials, application to a wide range of applications such as aerospace, aviation as well as automobiles is increasing. However, when a load is repeatedly applied to the structure, breakage occurs at the interface between the reinforcing fiber and the matrix resin, which is the weakest point in the composite material, which can lead to the destruction of the entire structure. It causes delamination. Therefore, studies on structural health monitoring using a sensor network that can identify and prevent defects in such composite materials in advance are being actively conducted.

In the existing structural integrity monitoring system, a strain gauge and a fiber Bragg grating sensor have been generally used.

In the case of a strain gauge, it is easy to attach and has a high sensitivity, but it cannot be used by embedding between laminae, and has a disadvantage in that numerous sensor nodes are required to detect micro-defects. The optical fiber Bragg grating sensor has an advantage that can be used as an insertion type, but there is a problem that it acts as another defect inside the composite material due to its large diameter and low mechanical properties compared to the reinforcing fiber.

To solve the problems of such existing systems, a conductive particle-based nanocomposite that has unique electromechanical properties and is free in physical property design depending on the combination of materials used can be used as an alternative method. . However, in the case of the conventional nanocomposite sensor, it is not suitable for the structural integrity monitoring system of the composite structure as most of the research is focused on improving the sensitivity as it is focused on the development of a sensor with flexible characteristics for application to the bio and wearable fields.

For example, Korean Patent Application Publication No. 10-2015-0046254 discloses a strain sensor having conductivity by forming nanowires on a substrate. However, in this case, since the substrate itself receives the applied load as it is, there is a disadvantage that it is not suitable for a structure having a high load.

Therefore, the sensor for structural integrity monitoring of a composite material structure has high mechanical properties so that it can be used as an insertion type without deteriorating the properties of the composite material, and has a low noise level and high linearity for stable strain sensing. It is a situation that requires the development of a strain sensor.

Accordingly, a problem to be solved by the present invention is to provide a strain sensor capable of supporting a load and having a noise level and linearity suitable for strain sensing of a composite material structure, and a method of manufacturing the same.

An embodiment of the present invention is a core-shell structure of a fiber-type strain sensor, the fiber support constituting the core; And a multilayered shell layer formed on the fiber support, wherein the shell layer comprises: a first elastomer formed on the fiber support; A conductive layer formed on the first elastomer; And a second elastomer formed on the conductive layer, wherein the sensor senses a strain rate of a structure including the sensor according to a change in resistance of the conductive layer.

More specifically, the conductive layer may have a sandwich structure in which at least two unit conductive layers having different conductivity are sequentially stacked.

In this case, the unit conductive layer includes conductive particles, and the two unit conductive layers may have different conductivity by varying the weight% of the different conductive particles. Specifically, the conductive layer includes a first unit conductive layer; A second unit conductive layer; And a sandwich structure including a first unit conductive layer, wherein the second unit conductive layer has a lower fraction of conductive particles than the first unit conductive layer.

The fiber support may be a single filament.

Meanwhile, the first elastomer and the second elastomer may have a higher Poison's ratio than the fiber support, and the first elastomer and the second elastomer may be polyurethane (PU), Polydimethylsiloxane (PDMS), natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), and ethylene vinyl acetate copolymer (EVA). It can contain either.

In addition, the conductive particles may include any one selected from the group consisting of carbon nanotubes, graphene, silver nanowires, and gold nanowires.

An embodiment of the present invention is a method for manufacturing a fiber-type strain sensor having a core-shell structure, comprising the steps of: coating a first elastomer on a fiber support; Coating a conductive layer of a sandwich structure on the first elastomer; And coating a second elastomer on the conductive layer, wherein the conductive layer of the sandwich structure has a structure in which unit conductive layers having different conductivity are sequentially stacked.

The coating may be performed by dipping or spraying.

In addition, the unit conductive layer includes conductive particles, and the two unit conductive layers may have different conductivity by varying the weight% of the different conductive particles.

In this case, the conductive layer is a first unit conductive layer; A second unit conductive layer; And a sandwich structure including a first unit conductive layer, wherein the second unit conductive layer may have a lower fraction of conductive particles than the first unit conductive layer, and the fiber support is a single filament. It is done.

According to the use of a multi-layered shell structure sensing layer including an ultra-high strength core fiber, an elastomer layer and a sandwich structure laminated conductive layer according to the present invention, the strength and rigidity are improved by the core fiber, and the noise level is reduced by the elastomer layer. It is possible to manufacture a fibrous sensor with improved linearity of the measurement signal by the conductive layer of the sandwich structure, so that it is possible to stably measure the strain rate without acting as a defect in the composite material structure. Therefore, it is possible to apply to a wider variety of fields by solving the problem of the existing sensor that was acting as a defect in the composite material structure, and has the advantage of obtaining a reliable measurement result.Since it can be manufactured continuously, the manufacturing cost is lower than that of existing sensors. There is an advantage that can be lowered.

1 is a schematic diagram showing the structure of a core-shell type fiber strain sensor according to an embodiment of the present invention.

2 is a diagram showing the configuration of a fiber-type strain sensor having a core-shell structure according to an embodiment of the present invention.

3 is a flow chart showing a process of a method for manufacturing a fiber-type strain sensor having a core-shell structure according to an embodiment of the present invention.

4 is a schematic diagram showing a dry jet wet spinning system used in manufacturing a fiber support in an embodiment of the present invention.

5 is a schematic diagram showing a coating process for forming a multilayered shell structure according to an embodiment of the present invention.

6 is a graph showing DSC analysis results of UHMWPE fibers prepared in Examples.

7 is a graph showing the mechanical properties of UHMWPE fibers prepared in Examples ((a) tensile strength, (b) tensile modulus).

8 is a graph showing the surface shape and electrical resistance of the fiber-type strain sensor prepared in Example ((a) the coating thickness and surface shape of the MWCNT layer, (b) the electrical resistance of the sensor fiber).

9 is a view showing the measurement result of the strain sensitivity of the fiber-type strain sensor.

10 is a diagram showing a circuit diagram of an electric network according to an embodiment of the present invention.

11 is a diagram showing SNR measurement values of the fiber-type strain sensors manufactured in Examples 1 and 3. FIG.

12 is a diagram showing a strain distribution diagram of a fiber-type strain sensor manufactured in Examples 1 and 3. FIG.

13 is a diagram showing radial strain in the MWCNT layer of the fibrous strain sensor prepared in Examples 1 and 3. FIG.

14 is a diagram showing a schematic diagram of an electrical network and a measurement value of ΔR/Ro for a time of 1000 cycles or more of the fibrous strain sensors manufactured in Examples 2 to 4. FIG.

15 is a diagram showing a hysteresis curve of DP-MC.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description.

However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the present invention, when it is determined that a detailed description of a related known technology may obscure the subject matter of the present invention, a detailed description thereof will be omitted.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present invention, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements, numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance the possibility of the presence or addition.

Hereinafter, the present invention will be described in detail.

Referring to FIG. 1, a core-shell type fiber strain sensor 1 according to an embodiment of the present invention includes a fiber support 10 forming a core; And a multi-layered shell layer 20 formed on the fiber support 10, wherein the shell layer 20 includes: a first elastic polymer 21 formed on the fiber support 10; A conductive layer 22 formed on the first elastomer 21; And a second elastomer 21 ′ formed on the conductive layer 22.

At this time, the core-shell type fibrous strain sensor 1 is characterized in that it senses the strain of the structure including the sensor according to the resistance change of the conductive layer 22.

In the core-shell type fibrous strain sensor 1 according to an embodiment of the present invention, strength and rigidity are improved by the fiber support 10 constituting the core, the noise level is improved by the elastomer, and the conduction Since the linearity of the measurement signal can be improved by the layer 22, the strain can be easily measured stably without acting as a defect in the composite material structure. For reference, in the case of a conventional sensor, when used as an insert type, it acts as a defect in the composite material, but the core-shell type fiber strain sensor 1 of the present invention to which a high strength core fiber is applied is a reinforcing fiber used in a composite material. It has the advantage of being able to reduce the difference in mechanical properties between and to maintain the structural reliability of the entire structure and to monitor the strain distribution inside the structure.

First, the fiber support 10 constituting the core may be a single filament, and an ultra high molecular weight polyolefin-based polymer (Ultra High Molecular Weight Polyethylene, UHMWPE) having excellent mechanical properties may be used. In addition, the fiber support 10 may be manufactured by using a wet process such as air-gap wet spinning and wet spinning in order to be manufactured in a fibrous shape.

Specifically, the initially spun fiber is stretched while passing between the hot stretching rollers, and mechanical properties can be maximized through alignment of molecular chains in the fiber longitudinal direction. At this time, the optimum processing conditions may be determined in a range between the melting point of the polymer material and the recrystallization temperature.

Next, the elastomer is uniformly coated on the surface of the fiber support 10, and may be coated by a method such as dip coating or spray coating. For example, it may be coated by a dip coating method.

The first elastomer 21 and the second elastomer 21 ′ are characterized by having a Poison's ratio higher than that of the fiber support 10.

Here, the term "Poisson's ratio" is a ratio of the transverse deformation and the longitudinal deformation when a vertical stress is applied to the material, and may mean an index of material behavior that is considered important in grasping the deformation in the elastic deformation region.

Specifically, the first elastomer 21 and the second elastomer 21 ′ include polyurethane (PU), polydimethylsiloxane (PDMS), natural rubber (NR), butadiene rubber (BR), It may include any one selected from the group consisting of styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), and ethylene vinyl acetate copolymer (EVA). The first elastomer 21 and the second elastomer 21 ′ may be made of the same elastomer, or may be made of different elastomers. For example, the first elastomer 21 and the second elastomer 21 ′ may be polyurethane (PU).

In particular, the first elastomer 21 and the second elastomer 21 ′ are compressed into the conductive layer 22 and the two

elastomer layers

21 and 21 ′ surrounding the conductive layer 22 to be described later. By inducing compressive deformation, it is possible to significantly reduce the noise level of the sensor by preventing breakage of the conductive network in the fiber radial direction.

In addition, the conductive layer 22 may have a sandwich structure in which at least two unit conductive layers 22 having different conductivity are sequentially stacked. Specifically, the unit conductive layer 22 includes conductive particles, and the two unit conductive layers 22 may have different conductivity by varying the weight% of the different conductive particles. More specifically, a layer having a high weight percent of conductive particles having a stable response characteristic and a layer having a low concentration having a high sensitivity may be alternately stacked. In particular, the electroconductive layer 22 having a sandwich structure may complement each other with characteristics of each layer due to the parallel connection effect, thereby implementing a sensor having excellent linearity and a sensitivity.

For example, the conductive layer 22 has a sandwich structure including a first unit conductive layer 221, a second unit conductive layer 222, and a first unit conductive layer 221, and the second unit conductive layer 222 ) May have a lower fraction of conductive particles than the first unit conductive layer 221.

The conductive particles may include any one selected from the group consisting of carbon nanotubes, graphene, silver nanowires, and gold nanowires, and for example, may be carbon nanotubes.

More specifically, the material of the conductive layer 22 may be an aqueous coating solution in which conductive particles are dispersed, and for more stable sensing, a coating solution in which conductive particles are dispersed in a thermoplastic polymer may be used. Furthermore, a desired characteristic can be designed by varying the stacking order and the number of stacking of the sandwich-type conductive layers 22. In the case of manufacturing the fibrous strain sensor 1 in this manner, it is possible to manufacture the fiber support 10 through the formation of the shell layer 20 in a continuous process, thereby reducing the manufacturing cost.

3 is a flow chart showing a process of a method for manufacturing a fiber-type strain sensor having a core-shell structure according to an embodiment of the present invention. Referring to FIG. 3, a method of manufacturing a fiber-type strain sensor 1 having a core-shell structure according to an embodiment of the present invention will be described.

Specifically, a method for manufacturing a core-shell structured fibrous strain sensor 1 according to an embodiment of the present invention includes the steps of coating a first elastomer 21 on the fiber support 10 (S100); Coating the conductive layer 22 having a sandwich structure on the first elastomer 21 (S200); And coating a second elastomer (21') on the conductive layer (22) (S300).

In this case, the conductive layer 22 of the sandwich structure may have a structure in which unit conductive layers 22 having different conductivity are sequentially stacked.

First, the fiber support 10 constituting the core may be a single filament, and an ultra high molecular weight polyolefin-based polymer (Ultra High Molecular Weight Polyethylene, UHMWPE) having excellent mechanical properties may be used.

In order to manufacture the fiber support 10, it may be manufactured using a wet process such as air-gap wet spinning and wet spinning. As an example, a spinning solution may be prepared by dissolving UHMWPE powder in a solvent, and the fiber support 10 may be prepared by using the dry-jet wet spinning method as the spinning solution.

In addition, the initially spun fiber is stretched while passing between the hot stretching rollers, and mechanical properties can be maximized through alignment of molecular chains in the fiber longitudinal direction. At this time, the optimum processing conditions may be determined in a range between the melting point of the polymer material and the recrystallization temperature.

Next, in each of the coating steps (S100, S200, S300), the coating process may be performed in a dipping or spray method, and for example, may be coated by a dip coating method.

The first elastomer 21 and the second elastomer 21 ′ have a Poison's ratio higher than that of the fiber support 10.

elastomer layers

In addition, the unit conductive layer 22 includes conductive particles, and the two unit conductive layers 22 may have different conductivity by varying the weight% of the different conductive particles. More specifically, a layer having a high weight percent of conductive particles having a stable response characteristic and a layer having a low concentration having a high sensitivity may be alternately stacked. In particular, the electroconductive layer 22 having a sandwich structure may complement each other with characteristics of each layer due to the parallel connection effect, thereby implementing a sensor having excellent linearity and a sensitivity.

The resulting core-shell structured fibrous strain sensor 1 forms a multilayer shell including an elastomer layer and a conductive layer 22 on the surface of the fiber support 10 having high strength and rigidity. When used as an insertion type in a composite structure, it is possible to measure the strain through detection of a change in resistance of the conductive layer 22 while improving the support for external loads such as tensile, compression, impact, or bending load.

Hereinafter, the present invention will be described in more detail through examples and experimental examples.

However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the contents of the present invention are not limited to the following Examples and Experimental Examples.

<실시예><Example>

실시예 1~4. 코어-쉘 구조의 섬유형 변형률 센서의 제조Examples 1-4. Fabrication of core-shell structured fibrous strain sensor

Fabrication of the fiber support forming the core

An ultra-high molecular weight polyolefin-based fiber support (core fiber) was prepared using a wet process. Specifically, the fiber support was manufactured using the dry jet wet spinning system shown in FIG. 4.

First, UHMWPE powder (U050: average molecular weight 5x10 ⁶ g/mol, Daehan Petrochemical) was mixed with paraffin oil (Sigma-Aldrich). In addition, in the subsequent dissolution process, it was maintained at 100° C. for 24 hours for a swelling process to improve the chain mobility of UHMWPE. The swollen UHMWPE powder was dissolved in paraffin oil at 170° C. for 4 hours to prepare a 4% by weight solution, and stored in a spinning solution syringe at this temperature for 2 hours to stabilize the molecular chain of the UHMWPE solution.

Next, the UHMWPE core fibers were spun using a dry-jet wet spinning method. Meanwhile, the UHMWPE solution was supplied to the nozzle at _{0.2 MPa of N 2} gas pressure to prevent thermal decomposition of the solution and uniformly extruded from the nozzle to prepare UHMWPE fibers.

And, the paraffin oil remaining in the UHMWPE fiber was removed.

Multi-layered shell layer formation

First, in order to maximize the mechanical properties of the manufactured UHMWPE fiber, it was subjected to hot stretching while passing through rollers having different speeds.

In addition, a multi-layered shell layer was formed on the UHMWPE fiber. 5 is a schematic diagram showing a coating process for forming a multilayered shell structure according to an embodiment of the present invention.

A method of forming a multilayered shell layer will be described with reference to FIG. 5.

First, the UHMWPE fibers were immersed in a PU aqueous solution (CRP 26301, T & L Co., Ltd), and after 20 seconds, the UHMWPE fibers were removed from the aqueous solution. Subsequently, the PU-coated fiber was dried at 80° C. for 3 minutes. This process was repeated 3 times.

In addition, a conductive layer was formed on the PU-coated UHMWPE fiber in the same manner as described above using an MWCNT aqueous solution (Kumho Petrochemical) (Examples 1 to 4). The structures of the conductive layers of Examples 1 to 4 are shown in Table 1 below. On the other hand, in the case of a sandwich structure conductive layer, the first unit conductive layer of 3% by weight MWCNT, the second unit conductive layer of 2% by weight MWCNT, and the third unit conductive layer of 3% by weight MWCNT are coated by the same coating procedure. Made it.

Subsequently, the UHMWPE fiber coated with the conductive layer was dried in an oven at 60° C. for 1 hour to remove excess water from the MWCNT layer.

Finally, a second PU layer was coated on the UHMWPE fiber on which the conductive layer was formed to prepare a fibrous strain sensor having a core-shell structure.

	MWCNT 층 구조MWCNT layer structure
실시예 1(SP-SC3)Example 1 (SP-SC3)	Single layer: 3wt%Single layer: 3wt%
실시예 2(DP-SC2)Example 2 (DP-SC2)	Single layer: 2wt%Single layer: 2wt%
실시예 3(DP-SC3)Example 3 (DP-SC3)	Single layer: 3wt%Single layer: 3wt%
실시예 4 (DP-MC)Example 4 (DP-MC)	Sandwich Multilayer: 3/2/3 wt%Sandwich Multilayer: 3/2/3 wt%

<실험예><Experimental Example>

실험예 1. UHMWPE 섬유의 DSC 분석Experimental Example 1. DSC Analysis of UHMWPE Fiber

DSC analysis of the UHMWPE fiber was performed, and the results are shown in FIG. 6.

6 shows the results of DSC analysis of spun UHMWPE fibers.

As a result, the crystallization and melting temperatures of the spun fibers were confirmed to be 119 and 133°C, respectively.

The mobility of polymer chains near the melting point of UHMWPE fibers is improved. In this case, the amorphous region of the fiber can be easily transferred to the crystal under external force and temperature.

In addition, when the heated fiber was cooled to near the crystallization temperature, recrystallization proceeded not only in the crystalline region but also in the amorphous region.

This phenomenon can improve the mechanical properties of UHMWPE fibers due to increased crystallinity and chain alignment.

실험예 2. UHMWPE 섬유의 기계적 특성 분석Experimental Example 2. Analysis of mechanical properties of UHMWPE fibers

The mechanical properties of the UHMWPE fibers prepared in the examples were analyzed. And, the results are shown in FIG. 7.

7 is a graph showing the mechanical properties of UHMWPE fibers prepared in Examples ((a) tensile strength, (b) tensile modulus)

Referring to FIG. 7, it can be seen that the tensile strength and modulus of the core fiber are improved as the draw ratio and hot stretching temperature increase. This seems to be because the crystallinity of the core-fiber is increased by rearrangement or rearrangement of the molecular chains during the hot drawing process.

In particular, the highest tensile strength and modulus appeared at the highest processing temperature, which was explained by the results of thermal analysis of the spun fibers.

실험예 3. 섬유형 변형율 센서의 표면 형태와 전기 저항 측정Experimental Example 3. Measurement of surface shape and electrical resistance of fiber-type strain sensor

The surface shape and electrical resistance of the fiber-type strain sensor prepared in Example were measured.

And, the results are shown in FIG. 8. 8 is a graph showing the surface shape and electrical resistance of the fiber-type strain sensor prepared in Example ((a) the coating thickness and surface shape of the MWCNT layer, (b) the electrical resistance of the sensor fiber).

First, Figure 8 (a) shows the surface shape of the coated fiber in relation to the coating sequence. Referring to FIG. 8(a), it can be seen that the MWCNT coating layer is uniformly formed on the fiber by a dip coating method. The thickness of the MWCNT coating layer was steadily controlled to 4 μm with various numbers of dip coatings.

And, Figure 8 (b) shows the electrical resistance measurement results of the fiber-type strain sensor. Referring to Fig. 8(b), it seems that the electrical resistance is related to the concentration of the MWCNT layer. Specifically, the electrical resistance seems to have decreased because the electrical path of DP-SC3 is densely formed compared to DP-SC2.

As a result, the weight-concentrated specimen appears to have a low electrical resistance value. In particular, the resistance value of the sandwich structured MWCNT layer specimen shows an intermediate result between DP-SC2 and DP-SC3 due to the combination of the low-concentration layer and the high-concentration layer.

실험예 4. 섬유형 변형율 센서의 감도 측정Experimental Example 4. Sensitivity measurement of fiber-type strain sensor

The sensitivity of the fiber-type strain sensor prepared in Example was measured.

And, the results are shown in FIG. 9. 9 is a view showing the measurement result of the strain sensitivity of the fiber-type strain sensor.

Referring to FIG. 9, in Examples 1 to 4, the sensitivity tends to increase. This is because a change in resistance of the conductive layer occurs due to the breakage of the conductive network due to the tensile load. In addition, when an external tensile load is applied to the sensor, the relative distance of the MWCNT increases. Accordingly, the total electrical resistance increased due to the disconnection of the MWCNT network.

9(a), (b) and FIG. 10, the single PU layer structure is more sensitive than the double PU layer structure, and the reason for the high sensitivity in the single PU layer structure is as shown in FIG. 10(a), This is because the distance between the CNTs increases rapidly due to the tensile deformation in the radial direction of the CNT layer, resulting in a rapid change in resistance. On the contrary, as shown in Figs. 10(b) and (c), when an external tensile load is applied, since compressive deformation occurs along the radial direction, the change in resistance to the double PU layer structure is relatively small.

Referring to FIG. 9(b), the fiber-type strain sensor of Example 2 shows the highest sensitivity and non-linear shape, which seems to be due to the low concentration of MWCNT. For reference, when the concentration of the MWCNT layer is low, the tunneling effect is superior to the direct contact of the MWCNT in the formation of the electric path, and the above phenomenon occurs. When one of the electrical paths is cut off by an external load, the total resistance of the conductive layer increases rapidly. On the other hand, in the case of the second embodiment, the sensitivity is sensitive, but the electrical path is weak, and the sensing response may be unstable.

In the case of Example 2, the GF fitting result also confirmed the nonlinear behavior of the sensor. Specifically, the GF value at 3 to 4% strain increased significantly over 161% over the 1 to 2% strain range.

Referring to FIG. 9(c), in the case of Example 3 (c), it can be seen that the linearity of the sensitivity curve was improved compared to Example 2 due to an increase in the MWCNT concentration. In addition, in the results of fitting the gauge factor (GF), the GF of Example 3 increased by 50% or more over the range of 1 to 2% strain. Example 3 showed a stable response with a lower noise level than Example 2 because the number of electrical paths increased as the MWCNT content increased. In Example 3, the maximum sensitivity was reduced by 55% compared to Example 2.

Based on the result of the sensitivity measurement of the optical fiber sensor having the mono-MWCNT layer structure, it was confirmed that the improvement of the linearity of the sensing response was limited using the single layer structure.

The linear response of the strain sensor is critical for accurate strain detection, signal processing and use. Therefore, in the experimental example, in order to improve the linearity of the sensing response, a sandwich-structured MWCNT layer was introduced.

As shown in Fig. 9(d), it can be seen from the result of the sensitivity measurement of the sensor fiber having the sandwich structured MWCNT layer, that the linear sensing response is improved. It can be seen that the combination of the MWCNT layers of different concentrations is effective in improving the linearity of the measurement signal.

실험예 5. 섬유형 변형율 센서의 SNR 값 측정Experimental Example 5. Measurement of SNR value of fiber-type strain sensor

The signal-to-noise ratio (SNR) value of the fiber-type strain sensor prepared in Examples 1 and 3 was measured.

And, the results are shown in FIG. 11. 11 is a view showing the SNR measurement value of the fiber-type strain sensor prepared in Examples 1 and 3. Here, SNR follows the following equation, and SNR measures the relative magnitude of signal-to-noise, which means that the larger the SNR, the less the noise effect.

Where S is the electrical resistance detection signal from the fiber sensor, and σ is the standard deviation of the electrical resistance detection signal.

Referring to FIG. 11, the average SNR value of DP-SC3 was 359% higher than that of SP-SC3, which means that the double PU layer reduces the noise level.

Referring to Figure 12, in the single PU layer of SP-SC3, the radial contraction of the core fiber due to the effect of Poisson pulls the MWCNT layer in the radial direction and tensile deformation occurs in the radial direction of the MWCNT layer, which is the electricity of the MWCNT layer. Network can be destroyed (a). On the other hand, in the double PU layer of DP-SC3, the compressive deformation is the radial direction of the MWCNT layer because the first PU layer between the MWCNT layer and the UHMWPE core fiber compensates for the effect of the core fiber shrinkage on the MWCNT layer by a low modulus of elasticity. Was created as (b). This effect can be confirmed by significant tensile deformation in the radial direction of the first PU layer due to Poisson shrinkage in the radial direction of the core fiber and the MWCNT layer, as shown in Fig. 12(b). This means that with reference to FIG. 11, the double PU layer has a positive effect on reducing the noise level of the fiber sensor by preventing the failure of the electrical network of the conductive layer.

13, the radial strain in the MWCNT layer of DP-SC3 is lower than the radial strain in the MWCNT layer of SP-SC3. Accordingly, with reference to FIGS. 11 and 12, it is possible to confirm the noise reduction effect due to the prevention of electrical network failure of the MWCNT layer by the double PU layer.

실험예 6. 섬유형 센서의 1000 사이클 이상의 시간에 대한 ΔR/Ro 값 측정Experimental Example 6. Measurement of ΔR/Ro value for a time of 1000 cycles or more of a fiber-type sensor

The ΔR/Ro values for 1000 cycles or more of the fibrous strain sensors prepared in Examples 2 to 4 were measured.

And, the results are shown in Fig. 14. 14 is a diagram showing a schematic diagram of an electrical network and a measurement value of ΔR/Ro for a time of 1000 cycles or more of the fibrous strain sensors manufactured in Examples 2 to 4. FIG. Here, Ro is the initial electrical resistance before applying a tensile load, and ΔR is the change in electrical resistance due to tensile deformation.

Referring to FIG. 14, a recoverable signal response was shown in all of Examples 2 to 4, which is due to the PU layer. In addition, the breakdown and reconstruction of the filtration network was stably repeated during the stretch release cycle due to the flexibility and stretchability of the PU layer.

The excellent adhesion properties of the PU layer were able to form a strong interfacial bond with the MWCNT layer, and the repeatability itself can be realized by the PU layer, but the stability of the electrical signal such as signal fluctuations affects the robustness of the electrical network of the MWCNT layer. Receive. For this reason, different signal patterns were observed in Examples 2 to 4 of the double PU layer.

More specifically, in DP-SC2, the sensing signal was unstable during the loading-unloading cycle because the conductive network was not completely restored after each cycle. In addition, the relative resistance change in the low strain range in the high cycle showed a non-monotonic response due to the corrugated structure (or buckle structure) of the MWCNT formed in the previous cycle (a). DP-SC3 showed a more stable response than DP-SC2, but the peak resistance gradually decreased by 10% after 1000 cycles (b). On the other hand, the reduction rate of the peak resistance between the beginning and the end of 100 cycles of DP-MC was less than 1% (c). This is because the multiple conductive MWCNT layers create a dense conductive filtration network, resulting in a stable signal response in the cycle test.

15 is a diagram showing a hysteresis curve of DP-MC.

Referring to FIG. 15, a single stretch-release cycle using DP-MC showed about 6% hysteresis, which is lower than the previously reported fibrous strain sensor.

The fiber-type strain sensor having a core-shell structure according to the present invention is recognized for its industrial applicability in a wide range of applications, such as aerospace, aviation, and automobile fields that require strain sensing of a composite structure.

Claims

A fiber-type strain sensor with a core-shell structure,

A fiber support forming a core; And

It includes a multi-layered shell layer formed on the fiber support,

The shell layer,

A first elastomer formed on the fiber support;

A conductive layer formed on the first elastomer; And

And a second elastomer formed on the conductive layer, wherein the sensor senses a strain of a structure including the sensor according to a change in resistance of the conductive layer.
The method of claim 1,

The conductive layer is a core-shell structure fiber-type strain sensor, characterized in that the sandwich structure in which at least two unit conductive layers having different conductivity are sequentially stacked.
The method of claim 2,

The unit conductive layer includes conductive particles, and the two unit conductive layers have different conductivity by varying the weight% of the different conductive particles.
The method of claim 3,

The conductive layer is

A first unit conductive layer;

A second unit conductive layer; And

A sandwich structure including a first unit conductive layer, wherein the second unit conductive layer has a lower fraction of conductive particles than the first unit conductive layer.
The method of claim 4,

The fiber support is a single filament (Single filament), characterized in that the core-shell structure of the fibrous strain sensor.
The method of claim 1,

The first elastomer and the second elastomer have a higher Poison's ratio than the fiber support.
The method of claim 6,

The first and second elastomers are polyurethane (PU), polydimethylsiloxane (PDMS), natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber ( NBR) and ethylene vinyl acetate copolymer (EVA), characterized in that it comprises any one selected from the group consisting of a core-shell structured fiber strain sensor.
The method of claim 3,

The conductive particles are carbon nanotubes, graphene, silver nanowires and gold nanowires, characterized in that it comprises any one selected from the group consisting of a core-shell structured fiber strain sensor.
A method for manufacturing a fiber-type strain sensor with a core-shell structure,

Coating a first elastomer on the fiber support;

Coating a conductive layer of a sandwich structure on the first elastomer; And

Coating a second elastomer on the conductive layer,

The conductive layer of the sandwich structure is a core-shell structure fiber-type strain sensor manufacturing method, characterized in that the structure in which unit conductive layers having different conductivity are sequentially stacked.
The method of claim 9,

The coating is a method of manufacturing a fibrous strain sensor having a core-shell structure, characterized in that the coating is performed in a dipping or spray method.
The method of claim 9,

The unit conductive layer includes conductive particles, and the two unit conductive layers have different conductivity by varying the weight% of the different conductive particles.
The method of claim 11,

The conductive layer is

A first unit conductive layer;

A second unit conductive layer; And

A sandwich structure including a first unit conductive layer, wherein the second unit conductive layer has a lower fraction of conductive particles than the first unit conductive layer.
The method of claim 9,

The fiber support is a single filament (Single filament), characterized in that the core-shell structure fibrous strain sensor manufacturing method.
The method of claim 9,

The first elastomer and the second elastomer have a higher Poison's ratio than the fiber support.
The method of claim 9,

The first and second elastomers are polyurethane (PU), polydimethylsiloxane (PDMS), natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber ( NBR) and ethylene vinyl acetate copolymer (EVA), characterized in that it comprises any one selected from the group consisting of a core-shell structure fibrous strain sensor manufacturing method.
The method of claim 9,

The conductive particles are carbon nanotubes, graphene, silver nanowires, and gold nanowires.